Math::Expr::MatchSet - Represents matches in algebraic expretions
  require Math::Expr::MatchSet;
  $s=new Math::Expr::MatchSet;
  $s->Set($pos,$match);
  $s->Get($pos);
  Two expretion can be matched in several ways, therefor we need to be 
  able to represent a set of matches keyed by the matchposition (the 
  subexpretion, where the match where found).
  Create a new MatchSet object.
$s->Set($pos, $match)
  Sets the match at $pos to $match.
$s->Add($pos, $match)
  Synonyme to Set.
  Inserts all mathes in the MatchSet £mset intho $s.
$s->SetAll($var, $obj)
  Sets the variable $var to $obj in all mathces in this set, and removes 
  all matches that already had a diffrent value for the variable $var.
  Generates a string representation of the MatchSet, used for debugging.
  Returns the Match at possition $pos.
  Returns the positions at which there excists a match.
Hey! The above document had some coding errors, which are
    explained below:
  - Around line 107:
- Non-ASCII character seen before =encoding in '£mset'. Assuming
      CP1252